In recent years, document data is created in a markup language, such as Extensible Markup Language (XML) (hereinafter, such document data is referred to as an XML data), and is used on various computers. Since XML can facilitate a supply of structured documents and structured data via, for example, the Internet, the use of XML is increasing even among different systems.
To designate a specific check position in XML data, a search query is used. This search query is a standard query language for XML data, and has a capability of describing a search formula for a complex tree structure of XML data.
Also in recent years, for searching XML data by using a search query, there is a technique of using a Binary Decision Diagrams (BDD) method to represent the search query with a binary tree and evaluating whether data relevant to the search query is present in the XML data.
Japanese Laid-open Patent Publication No. 2000-330786 discloses a technology of using a JUMP instruction to represent a BDD for writing into an instruction memory when a logical-circuit simulation is performed, thereby allowing a substitution operation at high speed.
However, to evaluate a complex search query with a plurality of logical variables and logical operators being combined together based on the BDD method, a process has to be performed for each logical variable, thereby disadvantageously increasing a processing time required for evaluation.
That is, when a complex search query is evaluated based on the BDD method, reducing the processing time required for evaluation is an important issue.